The present invention is generally directed to mounting input/output connectors on printed circuit boards. More particularly, the present invention is directed to a system for mounting connectors on PC boards in a dense fashion without the concomitant necessity of a large number of holes in the printed circuit board.
In certain printed circuit board designs in which electronic circuit chips are surface mounted to the boards, connections are made to the chips via a board edge connector. However, the present invention is not directed to such systems directly although it should be noted that the present invention is not inconsistent with the utilization of a board edge connector.
However, the present invention is particularly directed at those circumstances and situations in which a large number of connections are to be made to a printed circuit board, typically more connections than would be feasible with a board edge connector alone. In one particular embodiment of the present invention, the design employs a rectangular array of surface-mounted electronic circuit chips. In such a design, it is desirable to be able to access a large number of chip pins from the periphery of the chip, that is, at the chip site itself. Accordingly, in this design, there is provided a rectangular array of electronic circuit chips. The chips are surrounded by cable connectors which are also surface mounted to the printed circuit board.
In one design example, the rectangular array of chips is disposed as seven columns and nine rows of chip components. However, with a connector at virtually every one of the edges of the chips for interconnection purposes, this requires that 252 holes be drilled in the printed circuit board to facilitate attachment of the connectors.
However, it is to be particularly noted that the provision of or a requirement for a large number of holes in the printed circuit board has decided negatively consequences. In particular, the larger the number of holes present in a printed circuit board, the weaker the board will be and, concomitantly, will be more subject to bending and flexing both of which are qualities that are not desired in printed circuit boards containing electrically conductive patterns which could be broken. Furthermore, the presences of a large number of holes in a printed circuit board means that the design of the board will include more wire routing problems since a portion of the board is no longer available as a foundation for the desired electronic circuit paths. Additionally, a large number of holes in the printed circuit board for connecting the individual surface mount connectors is undesirable in that it takes longer to manufacture such a board and, additionally, it takes a longer time to assemble the components that are to be attached to the board.
Accordingly, it is seen that conventional approaches to attachment of surface mount connectors to printed circuit boards leaves a lot to be desired in terms of their requirements for large number of holes which must be provided in the printed circuit board. Such holes are seen to complicate wiring layout and design which are critical processes in the manufacture of printed circuit boards.
It is important to note that electronic circuit chips are contained almost entirely in square or rectangular packages. This naturally leads to circuit board placement in rectangular arrays in which a significant portion of the available wiring space on the board is to be found in the regions between the chips. In the present context, further constraints are introduced by the inclusion of large numbers of board level connectors. These connectors typically surround each chip and introduce many wiring barriers which are effectively walls which significantly inhibit layout and wiring design. The fact that the linear density of the connector is high (e.g. 25 mil lead spacing) in the regions of these board level connectors is a factor which contributes significantly to operation of the board connectors as barriers or walls to effective wiring. Thus, the presence of the board connectors very significantly exacerbates the wiring situation so that, especially in a rectangular array of chips and connectors, the board area in the region where four chip corners meet becomes extremely critical for wiring. Excess numbers of board holes in these corner areas impede, and in many cases, prevent the possibility of desired or needed board-level wiring. Thus, in certain circumstances, circuit boards with large numbers of on-board connectors can quickly become impossible to wire.